Why does monsoon rain cause waterlogging in cities every year?

Heavy downpours have continued over the past several days, triggering deadly landslides and flash floods in many parts of the country and, most disturbingly, waterlogging in major cities, including Dhaka and Chattogram, which has severely disrupted vehicular movement. As a result, normal life has nearly come to a standstill.

Chattogram on Tuesday recorded 412 mm of rainfall, the highest in around 45 years since 1983, when the city's precipitation reached 511 mm in a single day on August 4. This has not only affected normal life but also disrupted rail and air services, leaving thousands of commuters stranded.

Following the torrential rain, large parts of the port city's metropolitan area went under water, submerging major roads, railway tracks and low-lying neighbourhoods, as much of the city's drainage network, including canals and the piped sewerage system, overflowed, spilling water onto roads. Although the authorities opened sluice gates to facilitate the quick discharge of rainwater, the effort proved futile.

Consequently, severe waterlogging occurred in Halishahar, Agrabad, Katalganj, Panchlaish, Chawkbazar, Rampur, Jamalkhan, Kathgor, Kapasgola and several other areas. The situation has worsened further as the heavy rain has continued.

Meanwhile, Dhaka has also been experiencing light to heavy rainfall intermittently over the past few days. On Tuesday, the city recorded 46 mm of rainfall. The monsoon downpour has caused waterlogging in many areas, including Green Road, Karwan Bazar, Panthapath, Malibagh Railgate, Mouchak, Moghbazar, Rampura, Khilgaon, and Chowdhurypara.

Unfortunately, the country's two major cities�"Dhaka and Chattogram�"have been suffering from severe waterlogging every year soon after the onset of the monsoon. This persistent problem has continued for years, if not decades, with little being done by successive governments to address the situation.

Now, the question is why, every year during the monsoon, it has become a common occurrence for these two cities to suffer from waterlogging under the very nose of the authorities. Interestingly, the reasons are well known.

The primary cause of the crisis, no doubt, is the encroachment on city canals through which rainwater is drained from urban areas. Notably, Dhaka's drainage system, which once consisted of a 2,211-kilometre network of drains, has been severely degraded. The system originally comprised canals, lakes and other water bodies. Not too long ago, Dhaka had 65 natural canals. Today, that number has dwindled to just 26, and most of them are clogged with garbage or have been illegally occupied.

Similarly, Chattogram once had 104 canals, but the number has now fallen to only 57, although some of them are being restored under several ongoing projects. The good news is that, according to reports, at least four major projects have been undertaken to modernise Chattogram's drainage system.

The time has now come for the government agencies to recover the encroached canals and other water bodies to help city dwellers get rid of the recurring waterlogging that continues to plague the country's urban areas.